Many naturalists at the present day lay far too little stress, in my opinion, on the test of sterility; yet it is not improbable that distinct species of plants after a long course of cultivation and variation may have their mutual sterility eliminated, as we have every reason to believe has occurred with domesticated animals. Nor, in the case of plants under cultivation, should we be justified in assuming that varieties never acquire a slight degree of mutual sterility, as we shall more fully see in a future chapter when certain facts are given on the high authority of Gartner and Kolreuter. (10/138. Gartner 'Bastarderzeugung' 1849 s. 87 and s. 169 with respect to Maize; on Verbascum ibid s. 92 and 181; also his 'Kenntniss der Befruchtung' s. 137. With respect to Nicotiana see Kolreuter 'Zweite Forts.' 1764 s. 53; though this is a somewhat different case.)
The forms of C. pepo are classed by Naudin under seven sections, each including subordinate varieties. He considers this plant as probably the most variable in the world. The fruit of one variety (pages 33, 46) exceeds in value that of another by more than two thousand fold! When the fruit is of very large size, the number produced is few (page 45); when of small size, many are produced. No less astonishing (page 33) is the variation in the shape of the fruit, the typical form apparently is egg-like, but this becomes either drawn out into a cylinder, or shortened into a flat disc. We have also an almost infinite diversity in the colour and state of surface of the fruit, in the hardness both of the shell and of the flesh, and in the taste of the flesh, which is either extremely sweet, farinaceous, or slightly bitter. The seeds also differ in a slight degree in shape, and wonderfully in size (page 34), namely, from six or seven to more than twenty-five millimetres in length.
In the varieties which grow upright or do not run and climb, the tendrils, though useless (page 31), are either present or are represented by various semi-monstrous organs, or are quite absent. The tendrils are even absent in some running varieties in which the stems are much elongated. It is a singular fact that (page 31) in all the varieties with dwarfed stems, the leaves closely resemble each other in shape.]
Those naturalists who believe in the immutability of species often maintain that, even in the most variable forms, the characters which they consider of specific value are unchangeable. To give an example from a conscientious writer (10/139. Godron 'De l'Espece' tome 2 page 64.) who, relying on the labours of M. Naudin, and referring to the species of Cucurbita, says, "au milieu de toutes les variations du fruit, les tiges, les feuilles, les calices, les corolles, les etamines restent invariables dans chacune d'elles." Yet M. Naudin, in describing Cucurbita pepo (page 30), says, "Ici, d'ailleurs, ce ne sont pas seulement les fruits qui varient, c'est aussi le feuillage et tout le port de la plante. Neanmoins, je crois qu'on la distinguera toujours facilement des deux autres especes, si l'on veut ne pas perdre de vue les caracteres differentiels que je m'efforce de faire ressortir. Ces caracteres sont quelquefois peu marques: il arrive meme que plusieurs d'entre eux s'effacent presque entierement, mais ii en reste toujours quelques-uns qui remettent l'observateur sur la voie." Now let it be noted what a difference, with regard to the immutability of the so- called specific characters this paragraph produces on the mind, from that above quoted from M. Godron.
I will add another remark: naturalists continually assert that no important organ varies; but in saying this they unconsciously argue in a vicious circle; for if an organ, let it be what it may, is highly variable, it is regarded as unimportant, and under a systematic point of view this is quite correct. But as long as constancy is thus taken as the criterion of importance, it will indeed be long before an important organ can be shown to be inconstant. The enlarged form of the stigmas, and their sessile position on the summit of the ovary, must be considered as important characters, and were used by Gasparini to separate certain pumpkins as a DISTINCT GENUS; but Naudin says (page 20), these parts have no constancy, and in the flowers of the Turban varieties of C.